Electrically conductive material, emitter containing electrically conductive material, and method for its manufacture

Abstract

A method is provided for manufacture of an electrically conductive material, including the steps of: (a) providing a structure made of electrically conductive fibers, and (b) producing a carbon-based, electrically conductive matrix at least partially enveloping the electrically conductive fibers. Before or after producing the matrix, at least part of the electrically conductive fibers are interrupted in the direction of possible current flow. Electrically conductive materials obtained in corresponding manner are also provided. An emitter is specified that contains a transparent or translucent housing and an electrically conductive material according to the above. The electrically conductive materials have an increased electrical resistance. These allow emitters of virtually any length to be operated at customary line voltages.

1 .- 23 . (canceled) 
     
     
         24 . A method for manufacture of an electrically conductive material, the method comprising the steps of:
 a) providing a structure made of electrically conductive fibers; and   b) producing a carbon-based, electrically conductive matrix that at least partially envelopes the electrically conductive fibers;   wherein, before or after producing the matrix, at least part of the electrically conductive fibers are interrupted in a direction of possible current flow.   
     
     
         25 . The method according to  claim 24 , wherein the electrically conductive material has a carbon content of at least 95 mass %. 
     
     
         26 . The method according to  claim 24 , wherein the electrically conductive fibers are selected from carbon fibers, silicon carbide fibers, fibers having ceramic components, or a mixture of at least two of these. 
     
     
         27 . The method according to  claim 24 , wherein a specific electrical conductivity of the matrix is lower than that of the electrically conductive fibers. 
     
     
         28 . The method according to  claim 24 , wherein the matrix is produced by a high temperature treatment of a material selected from thermoplastic and duroplastic materials that envelopes the structure made of electrically conductive fibers in a temperature range of 600° C. to 1,500° C. 
     
     
         29 . The method according to  claim 28 , wherein the thermoplastic material is selected from polypropylene, polyamide, polybutyleneterephthalate, polyethyleneterephthalate, polycarbonate, polysulfone, polyphenylether, polyphenylenesulfide, polyetheretherketone, polyphthalamide, polyetherimide, polyethersulfone, and a mixture of at least two of these. 
     
     
         30 . The method according to  claim 28 , wherein the duroplastic material is selected from a vinylester resin, a phenol resin, an epoxide resin, and a mixture of at least two of these. 
     
     
         31 . The method according to  claim 24 , further comprising the steps of:
 c) providing the structure made up of electrically conductive fibers by a two-dimensional precursor structure containing electrically conductive fibers;   d) carbonizing fractions of the two-dimensional precursor structure that are not the electrically conductive fibers; and   e) interrupting at least a part of the electrically conductive fibers by introducing voids, optionally bore holes.   
     
     
         32 . The method according to  claim 31 , wherein the two-dimensional precursor structure is a tape cut-to-size before the carbonizing step. 
     
     
         33 . The method according to  claim 24 , wherein the structure made of electrically conductive fibers is selected from the group consisting of:
 a plurality of fiber bundles;   a woven material made of fibers or a plurality of fiber bundles or at least two of these;   a braided material made of fibers or a plurality of fiber bundles or at least two of these;   a knitted material made of fibers or a plurality of fiber bundles or at least two of these;   a knitted fabric made of fibers or a plurality of fiber bundles or at least two of these; and   a combination of at least two of these.   
     
     
         34 . The method according to  claim 33 , wherein, for production of the matrix, the structure made of electrically conductive fibers is enveloped with an enveloping material, and wherein a composite thus generated is cut-to-size appropriately before a subsequent step of graphitizing, such that at least part of the electrically conductive fibers are interrupted as seen in a direction of current flow through the electrically conductive material. 
     
     
         35 . The method according to  claim 34 , wherein a cutting edge defining a direction of longitudinal extension of the electrically conductive material,
 in a case of a woven material, is inclined at an angle of 20° to 70° with respect to a weft, or   in a case of a braided material, extends parallel to an edge of the braided material.   
     
     
         36 . The method according to  claim 34 , wherein the composite of electrically conductive fibers and enveloping material is obtained by mixing the electrically conductive fibers and the enveloping material as a two-dimensional precursor structure in the form of a prepreg. 
     
     
         37 . The method according to  claim 34 , wherein the composite of electrically conductive fibers and enveloping material is obtained by vapor deposition of the enveloping material onto the electrically conductive fibers as a two-dimensional precursor structure in a form of a deposition structure before being cut-to-size. 
     
     
         38 . The method according to  claim 34 , further comprising at least one of the following steps: reducing thickness of fiber bundles before introduction into the structure, and reducing thickness of the fiber bundles within the structure after production of the structure. 
     
     
         39 . The method according to  claim 34 , wherein an angle of twist between mutually crossing fibers or fiber bundles or both within the structure made up of electrically conductive fibers deviates from 90° in either case. 
     
     
         40 . The method according to  claim 24 , wherein carbon is removed from the electrically conductive material. 
     
     
         41 . An electrically conductive material obtained by the method according to  claim 24 . 
     
     
         42 . An electrically conductive material comprising:
 a) a structure made of electrically conductive fibers; and   b) an electrically conductive matrix which at least partially envelopes the electrically conductive fibers;   wherein the electrically conductive fibers exhibit higher specific conductivity than the electrically conductive matrix;   wherein the electrically conductive material extends in a direction of longitudinal extension; and wherein, viewed along the direction of longitudinal extension, at least part of the electrically conductive fibers within the material are interrupted at least once.   
     
     
         43 . An electrically conductive material according to  claim 42 , wherein at least one of the following is true of the electrically conducting fibers: the electrically conductive fibers are interrupted in the electrically conductive material as seen in the direction of longitudinal extension: the electrically conductive fibers extend in a direction inclined with respect to the direction of longitudinal extension; and the electrically conductive fibers have one or more voids introduced in them. 
     
     
         44 . An electrically conductive material according to  claim 42 , wherein at least 50 mass % of the fibers in the electrically conductive material have a fiber length of no more than 0.5 m. 
     
     
         45 . An emitter comprising:
 a) a transparent or translucent housing; and   b) an electrically conductive material according to  claim 42  arranged in the housing.   
     
     
         46 . The emitter according to  claim 45 , wherein the electrically conductive material has appropriate flexibility, such that the electrically conductive material can be bent into a circle and over its entire length about a radius of 1.0 m without fracturing the electrically conductive fibers and/or the matrix and/or without separating the electrically conductive fibers and the matrix. 
     
     
         47 . The emitter according to  claim 46 , wherein the flexibility is such that the electrically conductive material can be bent into a circle and over its entire length about a radius of 0.25 m without fracturing the electrically conductive fibers and/or the matrix and/or without separating the electrically conductive fibers and the matrix. 
     
     
         48 . The emitter according to  claim 45 , wherein electrical conductivity of the electrically conductive material, measured as electrical operating voltage per unit of length of the electrically conductive material, exceeds 150 V/m.